Method of leaching copper sulfide ores containing chalcopyrite

ABSTRACT

An object of the present invention is to provide a method of recovering copper from primary copper sulfide ores containing chalcopyrite as a main constituent under versatile conditions for real operation in all efficient and cost-effective manner. 
     A method of leaching copper sulfide ores, wherein the growth of microorganisms present on ore surfaces and in a leaching solution is inhibited and the pH of the leaching solution is adjusted to 1.5 or less upon leaching of copper from copper sulfide ores containing chalcopyrite, is provided.

TECHNICAL FIELD

The present invention relates to a method of efficiently recoveringcopper from copper sulfide ores and particularly from primary coppersulfide ores such as chalcopyrite.

BACKGROUND ART

The SX-EW (SX-EW: solvent extraction-electrowinning) method, which isknown as a method of recovering copper from copper ores, involveshydrometallurgy. In the method, copper is leached from copper ores withthe use of sulfuric acid or the like, copper is concentrated in theleaching solution with the use of an organic solvent, and electrolyticcopper is obtained via electrowinning. A typical solvent used for copperhydrometallurgy is sulfuric acid. Thus, target ores treated withhydrometallurgical processes have been limited to copper oxide ores thatare readily dissolved in sulfuric acid or the like. However, in general,there are fewer copper oxide ore reserves than copper sulfide orereserves. Thus, applicability of hydrometallurgical processes forextraction of copper from copper sulfide ores with large ore reserveshas been investigated.

Examples of known leaching methods for copper sulfide ores viahydrometallurgy include agitated leaching method of performing anagitated batch reaction with the use of sulfuric acid or hydrochloricacid and a heap leaching method of forming ore heaps, supplying sulfuricacid or hydrochloric acid to the tops of the ore heaps, and recoveringliquid dripping therefrom due to the gravity. However, operation withsuch heap leaching method takes several years with low copper recovery,resulting in poor efficiency. Further, a bacterial leaching method ofleaching copper with the help of activity of microorganisms has alsobeen used. The bacterial leaching method has been applied in practicefor the extraction of copper from secondary copper sulfide orescontaining chalcocite (Cu₂S), covellite (CuS), or the like, which havebeen found in secondary enriched zones of porphyry copper deposits.Recently, research and development of such leaching technology has beenfocused into the extraction of copper from primary copper sulfide orescontaining chalcopyrite (CuFeS₂), which most abundantly exist as copperresources.

However, chalcopyrite is so refractory that the copper leaching rate ofchalcopyrite is extremely slow in sulfuric acid. Therefore, a variety ofattempts have been made in order to improve the leaching rate. Forinstance, high temperature-pressure treatments (JP Patent No. 3046986,JP Patent Publication (Kokai) No. 2001-515145 A, and JP PatentPublication (Kokai) No. 2003-328050 A), the maintenance of a certainoxidation-reduction potential by adjusting iron content and the ratio oftrivalent irons to divalent irons (JP Patent Publication (Kokai) No.10-265864 A (1998)), the maintenance of a certain oxidation-reductionpotential by adding activated carbon and iron to a leaching solution (JPPatent Publication (Kokai) No. 2005-15864 A), and other techniques havebeen reported. Although aforementioned methods show some effect onimprovement of rate of chalcopyrite leaching, these methods are toocostly to apply them to industrial operation, due to requirement of highenergy consumption, reagents, and so on.

Meanwhile, it is also problematic that, as leaching progresses, theleaching rate is significantly lowered due to passivation phenomenoncaused by a coat formed on the ore surface with residual sulfur and/oran iron-derived substance from the ore. In addition, divalent iron,which is reported to be effective for promoting chalcopyrite leaching,is oxidized to trivalent iron with iron-oxidizing bacteria existing innature, resulting in inhibition of copper leaching. In order to avoidthis inhibition, there was a suggestion that an inhibitor for aniron-oxidizing bacterium, such as, sodium lauryl sulfate or tannic acid,be added to a leaching solution. However, contrary to their expectation,it has been reported that addition of such an inhibitor for aniron-oxidizing bacterium inhibits copper leaching (“Shigen to Sozai”(Journal of the Mining and Materials Processing Institute of Japan) vol.115, 1999, pp. 172-176). Therefore, in practice, there is no viabletechnology involving hydrometallurgy with the use of primary coppersulfide ores containing chalcopyrite.

DISCLOSURE OF THE INVENTION

In view of the aforementioned reasons, it is an objective of the presentinvention to provide a method of recovering copper from primary coppersulfide ores containing chalcopyrite as a main constituent underversatile conditions for real operation in an efficient andcost-effective manner.

As a result of intensive studies to achieve above objectives, theinventors of the present invention have found that leaching of copperfrom chalcopyrite can be significantly improved in a manner such thatthe growth of microorganisms present on ore surfaces and in a leachingsolution is inhibited and the pH of the leaching solution is adjusted to1.5 or less upon leaching of copper from primary copper sulfide orescontaining chalcopyrite. This has led to the completion of the presentinvention.

Specifically, the present invention encompasses the followinginventions:

-   (1) A method of leaching copper sulfide ores, wherein the growth of    microorganisms present on ore surfaces and in a leaching solution is    inhibited and the pH of the leaching solution is adjusted to 1.5 or    less upon leaching of copper from copper sulfide ores containing    chalcopyrite.-   (2) The method of leaching copper sulfide ores according to (1),    wherein the growth of microorganisms is inhibited by heating ores to    100° C. or more prior to leaching.-   (3) The method of leaching copper sulfide ores according to (1),    wherein the growth of microorganisms is inhibited by treating ores    with an agent capable of inhibiting the growth of microorganisms    prior to leaching.-   (4) The method of leaching copper sulfide ores according to (1),    wherein the growth of microorganisms is inhibited by adding an agent    capable of inhibiting the growth of microorganisms to a leaching    solution.-   (5) The method of leaching copper sulfide ores according to any one    of (1) to (4), wherein the microorganisms are chemoautotrophic    bacteria.

Hereinafter the present invention will be described in detail. Thepresent application claims the priority of Japanese Patent ApplicationNo. 2008-078405 filed on Mar. 25, 2008 and encompasses contentsdescribed in the specification and/or drawings of the patentapplication.

The method of leaching copper sulfide ores of the present invention ischaracterized in that the growth of microorganisms present on oresurfaces and in a leaching solution is inhibited and the pH of theleaching solution is adjusted to 1.5 or less upon leaching of copperfrom copper sulfide ores containing chalcopyrite.

The term “ores” as used herein and in the claims also includes oreconcentrates.

Copper sulfide ores as targets for the method of the present inventionmay be copper sulfide ores containing chalcopyrite as a main constituentor copper sulfide ores that partially contain chalcopyrite, for example.The chalcopyrite content is not particularly limited. However, in thecases of ores mainly comprising so-called secondary copper sulfide orescontaining chalcocite and covellite, the growth of microorganismspromotes copper leaching, which is contrary to the conditions of themethod of the present invention. Thus, it is preferable to use orescontaining moderate or low amounts of such secondary copper sulfideores, to use ores (residues) after the leaching treatment targeted tothe copper from secondary copper sulfide ores accompanied with thegrowth of microorganisms, or to subject secondary copper sulfide ores toa leaching treatment accompanied by the growth of microorganismsfollowing the leaching step of the present invention.

The method of the present invention can be applied in any types ofcopper-leaching operations using a sulfuric acid solution as a leachingsolution, for example, not only agitated batch leaching but also heap ordump leaching where copper is leached into sulfuric acid by irrigatingsulfuric acid over ores. In addition, leaching can be carried out atambient temperatures and does not particularly require heating or thelike. However, it is also possible to promote the leaching rate byheating.

According to the method of the present invention, methods for inhibitingthe growth of microorganisms and methods for sterilizing microorganismsthat are generally and widely used can be applied to the inhibition ofthe growth of microorganisms. Of these, the following methods arepreferably used as convenient and economical methods: a method whereinores are heat-treated prior to leaching; a method wherein ores aretreated with an agent capable of inhibiting the growth ofmicroorganisms; and a method wherein an agent capable of inhibiting thegrowth of microorganisms is added to a leaching solution.

In a case in which ores are heated before leaching, the heatingtemperature is not particularly limited, but it is preferably 100° C. ormore for efficient sterilization. In addition, as a heating method, avariety of means involving steam heating, heating with pressurization,and the like can be used in view of convenience, economic efficiency,sterilization efficiency, and the like. In addition, the upper limit ofheating temperature differs depending on heating methods to be used, butit is preferably 125° C. or less in a case of, for example,high-pressure steam sterilization.

Further, in a case in which ores are treated with an agent capable ofinhibiting the growth of microorganisms prior to leaching or an agentcapable of inhibiting the growth of microorganisms is added to aleaching solution, the type of agent to be used is not particularlylimited as long as the agent has the action of inhibiting the growth orproliferation of microorganisms. However, examples of such an agentinclude: compounds containing halogens such as fluorine, chlorine,bromine, and iodine, and salts thereof; compounds containing metals suchas silver, molybdenum, and cobalt, and salts thereof; alcohols such asethyl alcohol and methyl alcohol; phenols such as ethylphenol, xylenol,and chlorophenol; organic solvents such as acetone; invert soaps such asbenzalkonium chloride and benzethonium chloride; and organic acids suchas acetic acid. These agents are used at concentrations exceeding thelimiting concentration thereof at which the growth of microorganisms isinhibited.

In a case in which ores are treated with an agent capable of inhibitingthe growth of microorganisms prior to leaching, any method wherein anagent comes into contact with ores can be used. An example thereof is amethod involving dispersion of an agent. In such case, an agent ispreferably in a particle form in order to prevent it from being splashedupon dispersion, to allow it to be handled with ease, and to avoid itfrom being washed away by rain.

In addition, examples of a microorganism the growth of which isinhibited by one of the above methods include chemoautotrophic bacteriathat obtain energy by oxidizing inorganic compounds (e.g., hydrogensulfide, ammonia, and divalent iron ions), mainly includingiron-oxidizing bacteria, sulfur-oxidizing bacteria, denitrifyingbacteria, hydrogen bacteria, ammonia-oxidizing bacteria, andnitrite-oxidizing bacteria. Further, heterotrophic bacteria that obtainenergy by oxidizing organic compounds, nucleated microorganisms such asyeast and mold, and archaebacteria may also be included.

According to the method of the present invention, in addition to a meansfor inhibiting the growth of the above microorganisms, the pH of asulfuric acid solution serving as a leaching solution is adjusted to 1.5or less and preferably to between 1.0 and 1.5.

BEST MODES FOR CARRYING OUT THE INVENTION

Hereinafter, the present invention is more specifically described by wayof examples and comparative examples. However, the present invention isnot limited thereto.

EXAMPLE 1

A concentrate (mined in Chile) containing chalcopyrite as a mainconstituent was used as a target. The quality of the concentrate was asfollows: Cu=28% by mass; Fe=28% by mass; and S=32% by mass.

Three grams of the above concentrate was mixed with 300 mL of a leachingsolution (containing: ammonium sulfate=3 g/L; potassium hydrogenphosphate=0.5 g/L; magnesium sulfate heptahydrate=0.5 g/L; and potassiumchloride=0.1 g/L) that had been adjusted to a pH of 1.2 with sulfuricacid and poured into a 500 mL Sakaguchi flask. The flask was sterilizedby heating at 121° C. for 15 minutes, followed by shaking leaching at30° C. for 49 days. Then, the number of microorganisms (counted bymicroscopic observation with a counting chamber) and the copperconcentration in the leaching solution were determined.

COMPARATIVE EXAMPLE 1

Shaking leaching was performed at 30° C. as in Example 1, except that,prior to shaking leaching, a sulfur-oxidizing bacteriumAcidithiobacillus sp. TTH-19A strain (NITE BP-164) and an iron-oxidizingbacterium Acidithiobacillus ferrooxidans DSM 14882 strain (1.0×10⁷cells/mL each) were added, as autotrophic bacteria, to the flasksubjected to heat sterilization described in Example 1 and the bacteriawere allowed to grow simultaneously upon leaching. Then, the number ofmicroorganisms and the copper concentration in the leaching solutionwere determined.

COMPARATIVE EXAMPLE 2

Shaking leaching was performed at 30° C. as in Example 1, except thatthe pH of the leaching solution described in Example 1 was adjusted to1.8. Then, the number of microorganisms and the copper concentration inthe leaching solution were determined.

Table 1 lists the test results obtained in Example 1 and ComparativeExamples 1 and 2. Each result represents the average value obtained bycarrying out each experiment 2 or 3 times under the relevant conditions.In addition, oxidation-reduction potentials (ORPs) are values measuredwith the use of a silver/silver chloride reference electrode.

TABLE 1 ORP at the ORP pH at the beginning Cell Copper on beginning ofnumber on concentration day of leaching day 49 on day 49 49 leaching(mV) (cells/mL) (g/L) (mV) Example 1 1.21 356 0 2.8 388 Comparative 1.21356 2.3 × 10⁸ 1.2 407 Example 1 Comparative 1.85 340 0 0.7 338 Example 2

As shown by the above results, in a case in which the growth ofmicroorganisms present on ore surfaces and in a leaching solution wasinhibited and the pH of the leaching solution was adjusted to 1.5 orless (Example 1), the leaching rate of copper was significantly improvedcompared with a case accompanied by the growth of microorganisms(Comparative Example 1). Thus, the efficacy of the present invention wasconfirmed. In addition, in a case in which the pH of a leaching solutionexceeded 1.5 (Comparative Example 2), effects of improving the leachingrate of copper were not obtained, although the growth of microorganismspresent on ore surfaces or in the leaching solution was inhibited.

In Comparative Example 1, a decrease in the leaching rate of copper wasobserved, although a significant increase in the oxidation-reductionpotential (ORP) was not observed. Therefore, a decrease in the leachingrate of copper in a case in which the growth of microorganisms isobserved at a pH of 1.5 or less is mainly caused by microorganismsadhering to ores or those derived from the external environment,especially autotrophic microorganisms using sulfur compounds/ironcompounds as energy sources to grow, but not as a result of oxidizationof divalent iron to trivalent iron caused by iron-oxidizing bacteria aspreviously reported in “Shigen to Sozai” (Journal of the Mining andMaterials Processing Institute of Japan) vol. 115, 1999, pp. 172-176.

All publications, patents, and patent applications cited herein areincorporated herein by reference in their entirety.

INDUSTRIAL APPLICABILITY

According to the present invention, efficient leaching of copper fromcopper sulfide ores containing chalcopyrite can be achieved at ambienttemperature. With the method of the present invention, it is possible topromote a copper leaching rate by merely inhibiting the growth ofmicroorganisms and adjusting the pH of a leaching solution. Therefore,the method of the present invention is simple and highly cost-effective.

1. A method of leaching copper sulfide ores, wherein the growth ofmicroorganisms present on ore surfaces and in a leaching solution isinhibited and the pH of the leaching solution is adjusted to 1.5 or lessupon leaching of copper from copper sulfide ores containingchalcopyrite.
 2. The method of leaching copper sulfide ores according toclaim 1, wherein the growth of microorganisms is inhibited by heatingores to 100° C. or more prior to leaching.
 3. The method of leachingcopper sulfide ores according to claim 1, wherein the growth ofmicroorganisms is inhibited by treating ores with an agent capable ofinhibiting the growth of microorganisms prior to leaching.
 4. The methodof leaching copper sulfide ores according to claim 1, wherein the growthof microorganisms is inhibited by adding an agent capable of inhibitingthe growth of microorganisms to a leaching solution.
 5. The method ofteaching copper sulfide ores according to any one of claims 1 to 4,wherein the microorganisms are chemoautotrophic bacteria.